I've added a route into the and what I want to learn is why the routes are written in rc.local. which purpose or design is used for this. route s always written into rc.local.
route running when I restart server but if i run ( service network restart ) then route is not running added routes do not work then i run the systemctl start rc-local.service and route is running. this method is correct ? when the network is reset, I have to do this.
this method is correct for writing a permanent route. and what I want to learn is why the routes are written in rc.local. which purpose or design is used for this. routes always written into rc.local.

And if you are not using NetworkManager then you still don't use rc.local to add routes. That's what /etc/sysconfig/network-scripts/route-$interface and /etc/sysconfig/network-scripts/rule-$interface are for.